CVE-2020-20735
📋 TL;DR
This is a critical file upload vulnerability in LJCMS v4.3.R60321 that allows remote attackers to upload malicious files and execute arbitrary code on the server. Any organization running this specific version of LJCMS is affected, potentially leading to complete system compromise.
💻 Affected Systems
- LJCMS
📦 What is this software?
Ljcms by 8cms
⚠️ Risk & Real-World Impact
Worst Case
Complete server takeover with attacker gaining root/system-level access, data exfiltration, ransomware deployment, and persistent backdoor installation.
Likely Case
Webshell upload leading to data theft, defacement, and lateral movement within the network.
If Mitigated
Attack blocked at WAF/web application firewall level with file upload restrictions in place.
🎯 Exploit Status
Simple file upload bypass with publicly available proof-of-concept.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
1. Check for updated version from LJCMS vendor
2. If no patch, consider migrating to alternative CMS
3. Apply workarounds immediately
🔧 Temporary Workarounds
File Upload Restriction
allRestrict file uploads to specific extensions and implement server-side validation
# In web server config or .htaccess
<FilesMatch "\.(php|phtml|php3|php4|php5|phps|php7|php8|inc|pl|py|jsp|asp|aspx|sh|cgi)$">
Order Deny,Allow
Deny from all
</FilesMatch>
Directory Permissions
linuxSet upload directory to no-execute permissions
chmod -R 755 /path/to/upload/directory
chown -R www-data:www-data /path/to/upload/directory
🧯 If You Can't Patch
- Implement WAF rules to block malicious file uploads
- Disable file upload functionality entirely if not required
🔍 How to Verify
Check if Vulnerable:
Check LJCMS version in admin panel or via version file; if version is exactly 4.3.R60321, system is vulnerable.Check Version:
Check /ljcms/version.txt or admin panel version displayVerify Fix Applied:
Test file upload functionality with malicious extensions; verify uploads are properly validated and restricted.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads to /ljcms/index.php
- POST requests with file upload parameters
- Execution of unexpected PHP files in upload directories
Network Indicators:
- HTTP POST requests to /ljcms/index.php with file upload content
- Outbound connections from web server to unknown IPs
SIEM Query:
source="web_logs" AND uri="/ljcms/index.php" AND method="POST" AND (file_upload="true" OR contains(content_type, "multipart/form-data"))